[llvm-dev] Replacing a function from one module into another one

[Ahmad Nouralizadeh Khorrami via llvm-dev]

Hi Daniel,
The answer was for your first thread. The benefits are outlined in the
repository, but your problem is still there. I'm not sure. But this looks
similar to my recent problem. I think that a bitcast will solve the
problem. The types after the linking process may have different names but
the same contents. The links to the answers are as follows:
http://lists.llvm.org/pipermail/llvm-dev/2018-August/125413.html
https://stackoverflow.com/questions/51894129/convert-function-pointer-call-to-function-call-at-the-ir-level
Regards.

On Sun, 2 Sep 2018 at 23:30, Daniel Moya <danielmscr1994 at gmail.com> wrote:

> Hi Ahmad,
>
> What does that tool does besides what LLVM linker already does? I don't
> think my problem is in linking both modules, I think LLVM linker does the
> job for me, the issue is when changing the called function to call another
> function (in the example previously provided, to change it from foo2 to
> foo3, and adjusting the function parameter's references).
>
> Regards,
> Daniel Moya
>
> El dom., 2 de sep. de 2018 a la(s) 17:00, Ahmad Nouralizadeh Khorrami (
> ahmad.llvm at gmail.com) escribió:
>
>> Hi.
>> Besides the LLVM linker, you can also use this tool:
>> https://github.com/travitch/whole-program-llvm
>> It links all the modules and produces a single module containing every
>> function.
>> Regards.
>>
>> On Sun, 2 Sep 2018 at 16:57, Daniel Moya via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hello and thanks for the answer,
>>>
>>> I'm still facing issues, I'll do my best to explain my situation, as I
>>> explained, I have two modules, each one with its own main and functions, I
>>> would like to replace in the *oldModule* a function call that is
>>> calling *foo2* (defined in *oldModule*) to instead call *foo3*, which
>>> is defined in the *refModule.  *So in summary, I have:
>>>
>>>    1. The original instruction call, defined in the main function of
>>>    the oldModule, who is a calling function to foo2, I'll name it
>>>    *oInst *(original Instruction)
>>>    2. The "new" instruction call, defined in the main function of the
>>>    refModule, who is a calling function to foo3, I'll name it *nInst* (new
>>>    Instruction)
>>>    3. The foo2 function definition, defined in the oldModule, I'll name
>>>    it *oFunc *(original Function)
>>>    4. The foo3 function definition, defined in the refModule, I'll name
>>>    it *nFunc* (new Function)
>>>    5. I have the parameters (or arguments?) of both functions, both in
>>>    the calling instruction and in the function's definition, which I'll refer
>>>    to as *p(oInst)*, *p(nInst)*, *p(oFunc)*, *p(nFunc) *(the parameters
>>>    of)
>>>    6. For testing purposes, both foo2 and foo3 and defined identical,
>>>    same returning type, parameter's type and even the same variable's name in
>>>    the IR.
>>>
>>> So after calling the *llvm::LinkerlinkModules* function, I did:
>>>
>>> 1. First attempt:
>>>
>>>    1. llvm::CallInst *callOInst = static_cast<llvm::CallInst*>(oInst);
>>>    // I cast the* oInst* to a llvm::CallInst
>>>    2. callOInst->setCalledFunction(nFunc); // now *oInst* should call
>>>    nFunc
>>>
>>> Error:
>>> Call parameter type does not match function signature!
>>> %0 = load i32, i32* %a, align 4
>>> i32 %call1 = call i32 @foo3(i32 %0, i32 %1)
>>>
>>> So even though the parameters are the same type, and defined identically
>>> in both modules, the *p(oInst)* apparently does not match the *p(nFunc)*
>>> .
>>>
>>> 2. Second attempt:
>>>
>>>    1. llvm::Instruction *nCloneInst = nInst->clone(); //Clone of the
>>>    *nInst*, to avoid remove it from the refModule
>>>    2. nCloneInst->insertAfter(oInst); // I'll bring the nInst because I
>>>    know *p(nInst)* and *p(nFunc)* match
>>>    3. nCloneInst->mutateType(oInst->getType()); //Idk why I have to
>>>    this, but necessary for next line
>>>    4. oInst->replaceAllUsesWith(nCloneInst);
>>>    5. oInst->dropAllReferences();
>>>    6. oInst->eraseFromParent();
>>>
>>> Error:
>>> Instruction does not dominate all uses!
>>> %0 = load i32, i32* %a, align 4
>>> %2 = call i32 @foo3(i32 %0, i32 %1)
>>>
>>> Great, now the *p(nInst)* are still referring to their definition in
>>> the refModule, so either I bring those instructions too (which sounds
>>> really messy) or somehow I change the *p(nInst)* to refer to the
>>> instructions in oldModule, which in my case are actually defined the same
>>> (but apparently the references don't change based on the name being the
>>> same in both modules).
>>>
>>> 3. Third attempt:
>>>
>>>    1. The same 1-4 steps as before, from cloning instruction to
>>>    replaceAllUsesWith
>>>    2. llvm::CallInst *callNInst =
>>>    static_cast<llvm::CallInst*>(nCloneInst);
>>>    3. llvm::CallInst *callOInst = static_cast<llvm::CallInst*>(oInst);
>>>    // cast both *oInst* and *nInst*
>>>    4. for (unsigned int i = 0; i < callOInst->getNumArgOperands(); i++)
>>>    { callNInst->setArgOperand(i,callOInst->getArgOperand(i)); } //replace
>>>    *p(nInst)* with *p(oInst)*
>>>    5. The same 5-6 steps as before, drop and erase
>>>
>>> Error:
>>> Call parameter type does not match function signature!
>>> %0 = load i32, i32* %a, align 4
>>> i32  %2 = call i32 @foo3(i32 %0, i32 %1)
>>>
>>> So back to the first problem, the *p(nInst) *(now converted to
>>> *p(oInst)*) apparently does not match the *p(nFunc)*.
>>>
>>> I also looked into the *CloneFunctionInto *function, but I didn't
>>> understand the arguments of it, and there's really no documentation or
>>> examples that I could find on the internet. Specifically, I have troubles
>>> with *llvm::SmallVectorImpl< llvm::ReturnInst *> &Returns *argument, I
>>> don't know how to initialize it, it doesn't have a 0 argument constructor
>>> and if I try:
>>>
>>> llvm::SmallVectorImpl< llvm::ReturnInst *> ReturnsArg =
>>> llvm::SmallVectorImpl< llvm::ReturnInst *>(2); // Just as an example
>>>
>>> It says that constructor is protected. I didn't want to go further since
>>> I'm clueless on how to properly use this function, and I'm even not
>>> completely sure if it would fix all the troubles that I've been having with
>>> the other three attempts.
>>>
>>> Btw, all these errors happen when I try to run (through JIT) the module,
>>> a workaround that I know that I can do for all my attempts is just to dump
>>> the module to a file, and then reload it and execute it (I know it works
>>> since in both oldModule and refModule I use the same IR variable's names)
>>> but I would like to do the work the *right* way and not having to
>>> inefficiently dump a file just to reload it again and get all the
>>> references right.
>>>
>>> Thanks for the help in advance, I'll be really grateful for any advice
>>> or light in my situation.
>>>
>>> Regards,
>>> Daniel Moya
>>>
>>>
>>>
>>>
>>>
>>>
>>> El mar., 28 de ago. de 2018 a la(s) 20:26, Friedman, Eli (
>>> efriedma at codeaurora.org) escribió:
>>>
>>>> On 8/27/2018 10:37 AM, Daniel Moya via llvm-dev wrote:
>>>> > Hello LLVM Developers,
>>>> >
>>>> > I'm trying to replace a function defined in one module into another
>>>> > module (different files). The first issue I ran into was that
>>>> > llvm::Function does not have a method "moveBefore" or "moveAfter" as
>>>> > the llvm::BasicBlock or llvm::Instruction do, so I figured I would
>>>> > just move the BasicBlocks of the replacing function into the function
>>>> > that was being replaced, and then eliminate the original BasicBlocks.
>>>>
>>>> Cross-module operations are tricky in general; I'd suggest using the
>>>> Linker::linkModules API if possible.
>>>>
>>>> -Eli
>>>>
>>>> --
>>>> Employee of Qualcomm Innovation Center, Inc.
>>>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
>>>> Linux Foundation Collaborative Project
>>>>
>>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
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